Ready for an information dump? Here goes...
If you're planning to buy a professional brand like DSC, you should buy it from a company that provides warranty & technical support as pro security manufacturers won't support or help the end user. So a site like Amazon or any big box or drop ship seller, would be a poor choice since you wouldn't receive any technical support and if something fails you'll throw it in the garbage. I shop on Amazon all the time but Amazon is better suited for brands that are meant to be dead simple for DIY install and those that offer direct end user support & warranty.
For what it's worth, Aartech has been around since 2002, has the broadest range of security & automation products in Canada and is likely the only company in Canada willing to offer after sale support & warranty support for what they sell.
Before you go too far down the DSC rabbit hole, do a quick self-check and make sure you're willing to take the time to learn how to run the wires, connect the system, program it & troubleshoot it as there's a steep learning curve to pro systems like DSC. They're an excellent product but they're not designed to be easy to set up for a newbie so plan to invest time and you'll likely bang your head a few times during the process. Once they're up and running they are solid, stable, and relied on by pros.
Aartech offers a pre-programming service for DSC to help take some of the pain away from the install but it's still very hands on once the board, keypad, sensors, etc arrive on your doorstep.
If you can run wires for sensors you won't have to worry about batteries. Wired sensors are cheap but you'll pay instead for your time/labour.
Wireless sensors are more expensive and have batteries but they install in minutes.
If you plan to self monitor DSC look at Powerseries kits based on PC1616, PC1832 boards and add an EVL4 internet board. It uses a free cloud service to provide email or text alerts.
Yes, if the internet goes down you won't get messages. There is a "heartbeat" sent to the Eyezon (EVL4) cloud that can send a notice if the system doesn't report in for a while.
In a power failure, the alarm will have a battery backup, and if you have your modem/router & network gear on a UPS you'll have a window while things will still work. Eventually batteries will fail obviously.
If you want a backup plan in case the internet goes down - that's handled using cellular and at that point I'd suggest a monitoring company that can provide a cell backup. You'll pay a fee for their service & cell connection. Normally the cell backup has a similar battery life to the system so you'd have several hours (at least) of protection while power's out.
Food for thought - if you are concerned about wireless jamming, lines being cut, etc - and you feel you have a valid reason to be concerned, then you should pay for pro monitoring - and maybe pro install - to make sure you're well protected. Are you really a target for that sort of sophistication? Or is a bad guy more likely to smash a window, run in, grab some stuff and run away?
More food for thought. If you plan to install smoke or CO detectors - I personally suggest those must be professionally monitored. The monitoring company will call the fire dept without your intervention. Self monitoring means relying on a text message (ever miss one of those?). What if you're vacationing in Jamaica - who's reacting to a text or email for you?
If you choose to go pro - Aartech can either help with product & some support for DIY - or may be able to refer you to a trusted installer in your area that works with them.
You can also take a look at Ring - available at Aartech or all the big box stores. The Ring alarm is all wireless & uses Zwave for their sensors. They offer a free plan and you can pay them extra for monitoring & cell backup. It's probably one of the cheapest for this service. I would say it's more suited to a smaller home or condo but they do have repeaters available. The service plan also covers video doorbell cloud recording & camera cloud recording if you wanted to add cameras or a video doorbell- all in the same app.
Some other options - a VeraSecure hub with sensors & keypad & email alerts. Vera hubs support thousands of Zwave devices. VeraPlus adds Zigbee support. VeraSecure adds security functions and support for some 2Gig security sensors as well. They offer a cell backup service in USA but *not* Canada and I don't
know if they will in future so they are tied to Internet for now and they are NOT able to be pro monitored.
Likewise there is a neat little honeywell home system that looks like a tube - sits on the counter and has built in sensors and cameras. It can be used for free for DIY - but can't be monitored by a pro.
Additionally I highly recommend cameras and/or video doorbells. like a security system, stickers on the door, signs on the lawn - they act as a deterrent. Cameras can also provide some evidence in case of vandalism or a break-in. But get good cameras, make sure they're working properly and recording. Don't go cheap if you really want to have useful video.
Security is also about other things... like making sure your property is well lit and looks like less of a target than your neighbour
Check windows and doors. Did you reinforce your doors? A standard door has a fragile frame and it's really easy to kick it in. Or maybe the lock will be "bumped". Windows are fast and easy to break. Are any 2nd floor windows easy to get to? If put sensors on those windows too and/or a motion sensor in the master bedroom and/or hallway upstairs.
I'm not sure if direct links are frowned upon here so I won't post them unless asked but the Aartech site is full of security & camera products from diy & pro brands.
I hope this helps!